def validate(a, b):
"""
Validate that a => b.
"""
parser = ParserWrapper(Parser)
# Parse both expressions
a = parser.run([a])
b = parser.run([b])
if a.equals(b):
return VALIDATE_NOPROGRESS
# Evaluate a and b, counting the number of steps
# Optimization: if b is encountered while evaluating a, return
parser.set_root_node(a)
A = a
a_steps = 0
for i in xrange(MAXIMUM_REWRITE_STEPS):
obj = parser.rewrite()
if not obj:
break
# If b is some reduction of a, it will be detected here
if obj.equals(b):
return VALIDATE_SUCCESS
A = obj
a_steps += 1
if not A:
return VALIDATE_ERROR
parser.set_root_node(b)
B, b_steps = parser.rewrite_and_count_all()
if not B:
return VALIDATE_ERROR
# Evaluations must be equal
if not A.equals(B):
return VALIDATE_FAILURE
# If evaluation of b took more staps than evaluation of a, the step from a
# to b was probably useless or even bad
if b_steps >= a_steps:
return VALIDATE_NOPROGRESS
# Evaluations match and b is evaluated quicker than a => success
return VALIDATE_SUCCESS
def post(self):
try:
last_line = get_last_line(self)
if last_line:
parser = ParserWrapper(Parser)
response = parser.run([last_line])
if response:
response = parser.rewrite(include_step=True,
check_implicit=True)
if response:
hint, step = response
self.write({'step': str(step), 'hint': str(hint)})
return
self.write({'hint': 'No further reduction is possible.'})
except Exception as e:
self.write(format_exception(e))
def post(self):
try:
last_line = get_last_line(self)
if last_line:
parser = ParserWrapper(Parser)
response = parser.run([last_line])
if response:
response = parser.rewrite(include_step=True,
check_implicit=True)
if response:
hint, step = response
self.write({'step': str(step), 'hint': str(hint)})
return
self.write({'hint': 'No further reduction is possible.'})
except Exception as e:
self.write(format_exception(e))